Depending on diverse materials used for an active layer in a Thin Film Transistor (briefly called as TFT), TFTs can be classified into amorphous silicon TFTs, polycrystalline silicon TFTs, mono-crystalline silicon TFTs and metal oxide semiconductor TFTs. Metal oxide semiconductor TFTs have a higher carrier mobility, and can better meet the driving requirements of ultra large-scale liquid crystal displays. And, the metal oxide semiconductor TFTs also have the traits of uniform constituents, lower cost, higher transparency, etc., and thus attract a lot of attentions of research staff.
In prior art, when a metal layer for a source electrode and a drain electrode over a metal oxide semiconductor active layer is formed by etch, the metal oxide semiconductor active layer may often be etched by an etching liquid of the metal layer for the source electrode and the drain electrode, resulting in degradation of yield of metal oxide semiconductor TFTs. Therefore, it is necessary that an etch stop layer be formed over the metal oxide semiconductor active layer, acting to prevent the metal oxide semiconductor active layer from being corroded by the etching liquid of the source electrode and the drain electrode.
Currently, it is generally required that at least six patterning processes be used to manufacture a metal oxide semiconductor TFT array substrate having an etch stop layer, and they specifically include technological processes of forming a pattern layer that includes a gate electrode, forming a gate insulating layer, forming a metal oxide semiconductor active layer, forming an etch stop layer, forming a pattern layer that includes a gate electrode and a drain electrode, and forming a pixel electrode. And each patterning process includes film formation, exposure, development, etching, stripping and other process. Obviously, the more the patterning process is carried out, the higher the fabricating cost of the TFT array substrate is, and accordingly, this will cause the technological difficulty of fabrication of the TFT array substrate to increase. In turn, instability of the performance of the TFT array substrate may result, namely, it leads to a lower yield of the TFT array substrate. Therefore, how to decrease the number of patterning processes used in the manufacturing process of a metal oxide semiconductor TFT array substrate is an important technical problem that needs solving urgently.